The present invention relates to an improved immersion process for plating tin on ferrous, non-ferrous, or other electro-conductive substrates.
There are many prior art methods for electroplating and for electroless or immersion plating of tin or tin alloys upon substrates. However, interest has increased over the last several years toward electroless methods because of environmental concerns and energy costs. However, prior art immersion techniques have not been able to satisfactorily overcome one or more deficiencies such as extended processing time, the elimination of porosity of the tin coat or uneconomic processing conditions. Some prior processes require a permanent zinc undercoat on the substrate such as disclosed in U.S. Pat. No. 4,405,663.
While useful, this process does not produce a pore-free coating and is limited to plating over a zinc coated surface.
Other prior processes are not satisfactory in certain applications because the deposited coating is not pure tin but include other elements or compounds. Examples of such prior art include U.S. Pat. Nos. 3,971,861 and 4,194,913.
Further prior art drawbacks include porous or poorly adherent tin coats. Others are very limited in the thickness of the tin coat applied. Many prior processes require the immersion bath heated to relatively high temperatures to obtain economically practical rates of deposit. Some processes are subject to hydrogen embrittling of the substrate or are applicable to only a specific metal or narrow range of metal substrates.
The many prior attempts have yet to provide an electroless immersion process which produces a heavy, pure, pore-free and smooth, non-granular tin coating at efficient rates of deposit in a relatively simple and easily controlled process.